“The nuclear talks are complex and have entered a serious phase,” Mann said. Both sides “have agreed to keep the talks confidential in order to focus on the substance.”

“I believe there is a lot of work to be done,” Iran Foreign Minister Mohammad Javad Zarif told France 24 during a visit to Paris Tuesday. “We have made some progress, but there is a great deal of mistrust in Iran concerning the attitude, behavior and approach of some members of the P5+1.”

“I believe it is even possible to reach that agreement this week,” Zarif said, adding, however, that If “we don’t make a breakthrough at this round, it’s not a disaster.”

US officials, citing the seriousness of the new Iranian team and prospects for progress, have urged Congress to hold off on new Iran sanctions through the end of the year, arguing that a pause could help give momentum to intensified negotiations. In meetings with lawmakers, pro Israel groups and non-proliferations experts the past two weeks, Obama administration officials have said they are seeking to finalize an interim deal with Iran by January that would halt the advancement of Iran’s nuclear program, and then work out a comprehensive deal over the following six to 12 months.

“To the people of Israel, I want to say that the talks of the six world powers is the first step to stop the clock and prevent the nuclear program from going forward,” US Under Secretary of State Wendy Sherman told Israel’s Channel 10 in an interview Sunday November 3rd. “Thus we will have the time to discuss a broad agreement that treats all the issues that concern us.”

Possible elements of an interim deal would likely include Iran suspending 20% enrichment, as well as possibly halting the installation of more centrifuges, and suspending work towards bringing online the Arak heavy water reactor, in exchange for some sanctions relief and the possible release of some Iranian frozen hard currency assets in banks abroad, unconfirmed reports have suggested. US officials have said they will not dismantle the architecture of major oil and banking sanctions in an interim step, but presumably in a broader end state deal.

Israeli Prime Minister Benjamin Netanyahu, meeting with US Secretary of State John Kerry in Jerusalem Wednesday, warned against an interim deal with Iran that would loosen the sanctions regime.

“I’d be very worried of any partial deals that enable Iran to maintain those capabilities but begin to reduce sanctions because… I think this could undermine the longevity and durability of the sanctions regime,” Netanyahu said.

“Our goal is an Iran that has only a peaceful nuclear program,” Kerry said in remarks with Netanyahu Wednesday. “It is incumbent on us…to know with certainty that it is a peaceful program and there is no capacity to produce a weapon of mass destruction.”

Observers offered mixed assessments of how much progress to expect at this round of talks, scheduled for Thursday and Friday. Iran presented a proposal at a meeting with the P5+1 here last month (October 15-16), followed by technical talks in Vienna last week. Iran has also held two meetings with the International Atomic Energy Agency (IAEA), and has invited IAEA chief Yukiya Amano to come to Iran next week (November 11), though Amano had not yet confirmed his attendance.

“If there is political will on both sides, it would not be out of the question for the two sides to announce a general framework of a [confidence building measure] CBM agreement at the end of this week, with the promise that experts can then flesh out details in the next 30 days, or something like that,” a former western official told Al-Monitor Wednesday. “We have been discussing these issues for a while now — there should be no surprises.”